Chemical vapor deposition is defined as the formation of a non-volatile solid film on a substrate by the reaction of vapor phase reactants that contain desired components. The gases are introduced into a reactor vessel, and decompose and react at a heated surface on the wafer to form the desired film. Chemical vapor deposition is but one process of providing thin films on semiconductor wafers, such as films of elemental metals of compounds. It is a favored deposition process in many respects, principally because of its ability to provide highly conformal layers even within deep contacts and other openings.
One class of compounds finding increasing use in chemical vapor deposition of metals and metal compounds are organometallic precursors. Specifically, an example is the reaction of a titanium organometallic precursor of the formula Ti(N(CH.sub.3).sub.2).sub.4, named tetrakisdimethylamidotitanium (TDMAT) and ammonia in the presence of a carrier gas which reacts to produce TiN according to the following formula: EQU Ti(NR.sub.2).sub.4 +NH.sub.3 .fwdarw.TiN+organic by-products
Organometallic compounds contain a central or linking atom or ion (Ti in TDMAT) combined by coordinate bonds with a definite number of surrounding ligands, groups or molecules, with at least one of which is organic (the (N(CH.sub.3).sub.2 groups in TDMAT). The central or linking atom as accepted within the art may not be a "metal" in the literal sense. As accepted within the art of organometallic compounds, the linking atom could be anything other than halogens, the noble gases, H, C, N, O, P, S, Se, and Te.
The above and other chemical vapor deposition reactions involving organometallics are typically conducted at low pressures of less than 1 Torr. It is typically desirable in low pressure chemical vapor deposition processes to operate at as low a pressure as possible to assure complete evacuation of potentially undesirable reactive and contaminating components from the chamber. Even small amounts of these materials can result in a significant undesired increase in resistivity. For example, oxygen incorporation into the film before and after deposition results in higher resistivity. Additionally, it is believed that organic incorporation (specifically pure carbon or hydrocarbon incorporation) into the resultant film reduces density and resistivity. Such organic incorporation can result from carbon radicals from the organic portion of the precursor becoming incorporated into the film, as opposed to being expelled with the carrier gas. Carbon incorporation can also cause other undesired attributes in the deposited film, such as low density and poor long term reliability.
Hydrogen is a known capable reactant with deposited carbon or metal carbides. Such will react with carbon atoms to form volatile hydrocarbons. Hydrogen radicals are more reactive than elemental hydrogen or hydrogen ions in producing volatile hydrocarbons. Platinum is a known hydrogenation catalyst which produces hydrogen radicals from hydrogen or hydrogen compounds, such as is reported in Niemer et al., "Organometallic Chemical Vapor Deposition Of Tungsten Metal, And Suppression Of Carbon Incorporation By Codeposition Of Platinum", Applied Physics Letters (61)15 pp. 1793-95 (Oct. 12, 1992).
It would be desirable to improve upon these and other prior art chemical vapor deposition processes in producing layers having minimal incorporated carbon.